Look up this option.

File System Shield;
Expert options;
Scan when Opening;

Scan all files, radio.

Is it ticked or not?

If ticked. It will scan all executable files in full because these are the most likely to carry malware.

By default this option is off because when you open a folder. It usually is not needed to be on. But it is optional as extra security at scanning when opening such folders, containing executable files.